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Altera_Forum's avatar
Altera_Forum
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8 years ago

Best practices for verifying PWM (measuring time)...

Folks:

I am writing a testbench for a pulse-width modulator and wanted to check for several hundred different values. I figured I'd use a loop for each value, but I'm not sure of the best way to confirm (using assert) that the pulse is the correct length for each value. I was planning on just using a "wait until" and then "now - output'last_event" but I want to use the loop index in a comparison with a time value, which isn't going to work. I suppose I could use some sort of inner loop that counted the clock cycles, but that seems very clunky.

I'd appreciate any recommendations or links to good resources.

2 Replies

  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    8 years ago

    You can use the 'stable' VHDL attribute with a value consistent with the pwd command.

    Example:

    assert pwm_out'stable(TIME) report "signal is not stable during the expected time" severity error;